Ice cubes are frequently being added to people's drinks or used for various cooling purposes A wide variety of ice makers have been developed and marketed. Many of them focus on faster ice making speed and automation to enable users to get the ice cubes whenever needed. R.O.C. patent publication No. 330978 entitled “Automatic ice making apparatus and freezer” includes a water supply trough, an ice making tray and a water supply pump. The water supply rough is located in a freezer at a desired position and built with an improved structure, and a control procedure is provided for the automatic ice making apparatus. Another R.O.C. patent publication No. 396264 entitled “Ice making control apparatus for thermoelectric modular refrigerators” has a main heat exchanger and an auxiliary heat exchanger. The main heat exchanger includes a first thermoelectric module and a second thermoelectric module. The main heat exchanger and a plurality of heat exchange portions in the auxiliary heat exchanger can perform heat transfer to produce ice. The auxiliary heat exchanger receives a constant voltage. The voltage supplying to the main heat exchanger is determined by detecting the temperature of the freezer and the temperature difference thereof. When the temperature difference increases the voltage supplied to the main heat exchanger also is boosted. Otherwise the voltage is lowered. In other words, it adjusts ice making speed by altering the voltage through detection of the temperature of the freezer. Yet another R.O.C. patent No. M284863 entitled “Ice maker structure” includes an ice making module, a compressor equipped with a heat exchanger and an ice collection barrel. The ice making module has an ice making trough. The compressor is connected to a refrigerant pipe. Through the compressor and the refrigerant pipe temperature can be lowered to freeze the water in the ice making trough to become ice cubes. All the aforesaid conventional techniques try to accelerate ice making speed through the compressor or heat exchangers to lower the temperature faster. Trying to further speed up the cooling effect encounters many problems such as lack of space or increasing electric power consumption.